Of course in case the longer city covers the whole row then the next row can be colored with just two colors, and the row after that also can be colored with two colors but with two different colors than the ones just used on the previous row.
if a=blue, b=green, c=red, d=yellow
[d d d d d d d d d d d d] [a b a b a b a b a b a b] [c d c d c d c d c d c d]
4 color solution does not work if the map has one country whose horizontal length is longer than the rest of the countries on a map, and if there is at least one column of countries at the end of such a country, because any countries above or below it can be colored according to the 4 color rule, and any countries to the leftside of it are already colored according to the 4 color rule.
So, if the country with longer length sits at the rightmost place on a map so that there are no more columns of countries to its rightside, then 4 color solution works.